Spheroid sample cell for spectrometer

A sample cell for a spectrometer, and a spectrometer using such a sample cell. The sample cell may include a housing having a reflective inner surface which is at least a section of a spheroid bounding a cavity. A lens system receives electromagnetic radiation from a source and directs a converging beam through a port in the cavity to a focal point inside the cavity, such that the beam undergoes multiple reflections on the inner surface before exiting the cavity. Arrangements for adjusting beam cross-sectional area and angle are optionally provided. Methods which can be performed on such an apparatus and computer program products for performing such methods are further provided.